AU2016374421B2 - Method for selecting rail steel and wheel steel - Google Patents
Method for selecting rail steel and wheel steel Download PDFInfo
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/04—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for rails
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Abstract
Provided is a method for selecting rail steel and wheel steel, whereby fatigue damage of a railway wheel and a rail used in a railway track can be suppressed, and the service life of both the rail and the wheel can be extended. A method for selecting rail steel and wheel steel, for selecting rail steel having a composition containing, in terms of mass%, 0.70% to less than 0.85% C, 0.10% to 1.50% Si, 0.40% to 1.50% Mn, and 0.05% to 1.50% Cr, the remainder comprising Fe and unavoidable impurities, and wheel steel having a composition containing, in terms of mass%, 0.57% to less than 0.85% C, 0.10% to 1.50% Si, 0.40% to 1.50% Mn, and 0.05% to 1.50% Cr, the remainder comprising Fe and unavoidable impurities, so that when the rail steel and the wheel steel are used as a rail and a wheel in an actual railway, the yield strength YS
Description
METHOD FOR SELECTING RAIL STEEL AND WHEEL STEEL
TECHNICAL FIELD [0001] The present disclosure relates to a method for selecting a rail steel and a wheel steel that is capable of suppressing fatigue damage in a rail and a railway wheel used in a railway track and of extending the service life of both the rail and the wheel by controlling the ratio of the yield strength at a head portion of the rail to the yield strength at a rim portion of the wheel.
BACKGROUND [0002] In heavy haul railways mainly built to transport ore, the load applied to the axle of a freight car is much higher than that in passenger cars, and rails and wheels are used in increasingly harsh environments. For rails and wheels used under such circumstances, conventional rail steels primarily have a pearlite structure from the viewpoint of the importance of wear resistance and have a yield strength of 800 MPa or less, which may vary depending on the operating environment. Similarly, wheel steels having a yield strength of 500 MPa or less are conventionally used for railway wheels.
[0003] In recent years, however, in order to improve the efficiency of transportation by railway, the loading weight on freight cars is becoming larger and larger, and consequently, there is a need for further improvement of durability of rail steels and wheel steels. It is noted that heavy haul railways are railways where trains and freight cars haul large loads (loading weight is about 150 tons, for example).
[0004] Under such circumstances, for example, JP2004315928A (PTL 1) proposes a wheel for high-carbon railway vehicles in which wear resistance and thermal crack resistance are improved by increasing the C content to 0.85 % to 1.20 %. JP2013147725A (PTL 2) proposes a method for reducing the wear of rails and wheels by controlling the ratio of the rigidity of the rail steel and the hardness of the wheel steel.
CITATION LIST
Patent Literature [0005] PTL 1: JP2004315928A
PO163542-PCT-ZZ (1/31)
-22016374421 11 Jul 2019
PTL 2: JP2013147725A [0006] On the other hand, as described above, since the operating environments of rails and wheels are becoming more severe, rails and wheels suffer from fatigue damage. In particular, in curve sections of a heavy haul railway, it is required to suppress fatigue damage resulting from the rolling stress exerted by wheels and the sliding force due to centrifugal force.
[0007] However, in the technique described in JP2004315928A (PTL 1), although the wear resistance and the thermal crack resistance of the wheel are improved to some extent, the C content is as high as 0.85 % to 1.20 %, which makes it difficult to improve fatigue damage resistance. This is because as a result of steel containing a large amount of C, a proeutectoid cementite structure is formed depending on heat treatment conditions and the amount of cementite phase contained in a pearlite lamellar structure increases.
[0008] Further, in PTL 2, since attention is paid only to the relationship between the rail and the hardness of the wheel (Vickers hardness), although it is possible to suppress wear, it is difficult to suppress fatigue damage.
[0009] It would thus be helpful to provide a method for selecting a rail steel and a wheel steel that is capable of suppressing fatigue damage in a rail used in a railway track and of a railway wheel, and that can extend the service life of both the rail and the wheel.
SUMMARY OF THE INVENTION [0010] In order to address the above issues, we made rail steels and wheel steels with varying contents of C, Si, Mn, and Cr, and extensively investigated the relationship between yield strength and fatigue damage resistance. Our investigations revealed that by setting the ratio YSr/YSw of the yield strength YSr at a head portion of a rail and the yield strength YSw at a rim portion of a wheel to 0.85 or more and 1.95 or less, it is possible to suppress the fatigue damage in the rail and the wheel.
[0011] The present disclosure is based on the findings described above and has the following primary features.
1. A method for selecting a rail steel and a wheel steel comprising: selecting a rail steel and a wheel steel to be used as a rail and a wheel on an actual track, respectively, the rail steel having a chemical composition
PO163542-PCT-ZZ (2/5)
-3 2016374421 11 Jul 2019 containing, by mass%, C: 0.70 % or more and less than 0.85 %, Si: 0.10 % to 1.50 %, Mn: 0.40 % to 1.50 %, and Cr: 0.05 % to 1.50 %, with the balance of Fe and inevitable impurities, the wheel steel having a chemical composition containing, by mass%, C: 0.57 % or more and less than 0.85 %, Si: 0.10 % to
1.50%, Mn: 0.40 % to 1.50 %, and Cr: 0.05 % to 1.50 %, with the balance of
Fe and inevitable impurities, such that the rail comprises a head portion having a yield strength YSr of 830 MPa or more, the wheel comprises a rim portion having a yield strength YSw of 580 MPa or more, and a ratio YSr/YSw of the yield strength YSr at the head portion of the rail to the yield strength
YSw at the rim portion of the wheel falls within a range of:
0.85 < YSr/YSw < 1.95 (1).
[0012] The method for selecting a rail steel and a wheel steel according to 1. 15 above, wherein the chemical composition of the rail steel further contains, by mass%, at least one selected from Cu: 1.0 % or less, Ni: 1.0 % or less, V: 0.30 % or less, Nb: 0.05 % or less, Mo: 0.5 % or less, W: 0.5 % or less, Al: 0.07 % or less, Ti: 0.05 % or less, and B: 0.005 % or less.
[0013]
The method for selecting a rail steel and a wheel steel according to 1. or 2. above, wherein the chemical composition of the wheel steel further contains, by mass%, at least one selected from Cu: 1.0 % or less, Ni: 1.0 % or less, V: 0.30 % or less, Nb: 0.05 % or less, Mo: 0.5 % or less, W: 0.5 % or less, Al: 0.07 % or less, Ti: 0.05 % or less, and B: 0.005 % or less.
[0014] According to the present disclosure, by using a rail steel and a wheel steel having predetermined chemical compositions and by controlling the ratio of the yield strength of the resulting rail to that of the resulting wheel, it may be possible to suppress the fatigue damage in the rail and the wheel, lengthening the service life of both.
BRIEF DESCRIPTION OF THE DRAWING
PO163542-PCT-ZZ (3/5)
-4[0015] FIG. 1 schematically illustrates a fatigue damage test method.
DETAILED DESCRIPTION [0016] Detailed description is given below. In the present disclosure, it is important that a rail steel and a wheel steel have the above-described chemical compositions. The reasons for limiting the chemical compositions as stated above are described first. The unit of the content of each component is mass%, but it is abbreviated as %.
[0017] [Chemical Composition of Rail Steel]
C: 0.70 % or more and less than 0.85 %
C is an element that forms cementite in a pearlite structure and has the effect of securing yield strength and fatigue damage resistance. If the C content is less than 0.70 %, the yield strength decreases, making it difficult to obtain excellent fatigue damage resistance. On the other hand, when the C content is 0.85 % or more, pro-eutectoid cementite is formed at austenite grain boundaries at the time of transformation after hot rolling, and the fatigue damage resistance is remarkably deteriorated. Therefore, the C content is set to 0.70 % or more and less than 0.85 %.
[0018] Si: 0.10 % to 1.50 %
Si is an element that is added as a deoxidizer and as a pearlite-structure-strengthening element. To obtain the addition effect of Si, the Si content needs to be 0.10 % or more. On the other hand, a Si content beyond 1.50 % leads to an excessive increase in the yield strength, which ends up making the counterpart material, the wheel steel, prone to fatigue damage. Therefore, the Si content is set in a range of 0.10 % to 1.50 %.
[0019] Mn: 0.40 % to 1.50 %
Mn is an element that contributes to achieving high yield strength of the rail by decreasing the pearlite transformation temperature to refine the lamellar spacing. When the Mn content is below 0.40 %, however, this effect cannot be obtained sufficiently. On the other hand, a Mn content beyond 1.50 % leads to an excessive increase in the yield strength, which ends up making the counterpart material, the wheel steel, prone to fatigue damage. Therefore, the Mn content is set in a range of 0.40 % to 1.50 %.
[0020] Cr: 0.05 % to 1.50 %
PO163542-PCT-ZZ (4/31)
-5 Cr is an element that has the effect of increasing the pearlite equilibrium transformation temperature to refine the lamellar spacing and improving the yield strength by solid solution strengthening. When the Cr content is below 0.05 %, however, sufficient yield strength cannot be obtained. On the other hand, a Cr content beyond 1.50 % leads to an excessive increase in the yield strength, which ends up making the counterpart material, the wheel steel, prone to fatigue damage. Therefore, the Cr content is set to 0.05 % to 1.50 %.
[0021] The rail steel in one embodiment of the present disclosure has a chemical composition containing the above components with the balance of Fe and inevitable impurities. Examples of the inevitable impurities include P and S, and up to 0.025 % of P and up to 0.025 % of S are allowable. On the other hand, a lower limit for the P content and the S content may be 0 % without limitation, yet the lower limit is more than 0 % in industrial terms. In addition, since excessively reducing the contents of P and S leads to an increase in the refining cost, the P content and the S content are preferably 0.0005 % or more. The chemical composition of the rail steel of the present disclosure preferably consists of the above components and the balance of Fe and inevitable impurities, or alternatively, in addition to these, optional components as specified below. However, rail steels containing other trace elements within a range not substantially affecting the action and effect of the present disclosure are also encompassed by the present disclosure.
[0022] Optionally, the chemical composition of the rail steel may further contain, by mass%, at least one selected from the group consisting of Cu: 1.0 % or less, Ni: 1.0 % or less, V: 0.30 % or less, Nb: 0.05 % or less, Mo: 0.5 % or less, W: 0.5 % or less, Al: 0.07 % or less, Ti: 0.05 % or less, and B: 0.005 % or less.
[0023] V: 0.30 % or less
V is an element that has the effect of improving the yield strength by dispersing and precipitating in the matrix by forming carbides or nitrides. On the other hand, a V content beyond 0.30 % leads to an excessive increase in the yield strength, which ends up making the counterpart material, the wheel steel, prone to fatigue damage. Also, since V is an expensive element, the cost of rail steel increases. Therefore, in the case of adding V, it is
PO163542-PCT-ZZ (5/31)
-6preferable to set the V content to 0.30 % or less. The lower limit of the V content is not particularly limited, yet from the viewpoint of improving the yield strength, it is preferable to set the V content to 0.001 % or more.
[0024] Cu: 1.0 % or less
Like Cr, Cu is an element having the effect of improving the yield strength by solid solution strengthening. However, when the Cu content exceeds 1.0 %, Cu cracking is liable to occur. Therefore, in the case of adding Cu, it is preferable to set the Cu content to 1.0 % or less. The lower limit of the Cu content is not particularly limited, yet from the viewpoint of improving the yield strength, it is preferable to set the Cu content to 0.001 % or more.
[0025] Ni: 1.0 % or less
Ni is an element that has the effect of improving the yield strength without deteriorating the ductility. In addition, in the case of adding Cu, it is preferable to add Ni because Cu cracking can be suppressed by the addition of Ni in combination with Cu. When the Ni content exceeds 1.0 %, however, the quench hardenability increases and martensite is formed, with the result that the fatigue damage resistance tends to decrease. Therefore, in the case of adding Ni, it is preferable to set the Ni content to 1.0 % or less. The lower limit of the Ni content is not particularly limited, yet from the viewpoint of improving the yield strength, it is preferable to set the Ni content to 0.001 % or more.
[0026] Nb: 0.05 % or less
Nb bonds to C or N in the steel to form precipitates as carbides, nitrides, or carbonitrides during and after rolling, and effectively acts to increase the yield strength. Therefore, by adding Nb, the fatigue damage resistance can be greatly improved and the service life of the rail can be further extended. However, a Nb content beyond 0.05 % leads to an excessive increase in the yield strength, which ends up making the counterpart material, the wheel steel, prone to fatigue damage. Therefore, in the case of adding Nb, it is preferable to set the Nb content to 0.05 % or less. The lower limit of the Nb content is not particularly limited, yet from the viewpoint of improving the yield strength, it is preferable to set the Nb content to 0.001 % or more.
[0027] Mo: 0.5 % or less
Mo is an element having the effect of improving the yield strength by solid
PO163542-PCT-ZZ (6/31)
-7solution strengthening. However, a Mo content beyond 0.5 % leads to an excessive increase in the yield strength, which ends up making the counterpart material, the wheel steel, prone to fatigue damage. Therefore, in the case of adding Mo, it is preferable to set the Mo content to 0.5 % or less. The lower limit of the Mo content is not particularly limited, yet from the viewpoint of improving the yield strength, it is preferable to set the Mo content to 0.001 % or more.
[0028] W: 0.5 % or less
W is an element having the effect of improving the yield strength by solid solution strengthening. However, a W content beyond 0.5 % leads to an excessive increase in the yield strength, which ends up making the counterpart material, the wheel steel, prone to fatigue damage. Therefore, in the case of adding W, it is preferable to set the W content to 0.5 % or less. The lower limit of the W content is not particularly limited, yet from the viewpoint of improving the yield strength, it is preferable to set the W content to 0.001 % or more.
[0029] Al: 0.07 % or less
Al bonds to N in the steel to form precipitates as nitrides during and after rolling, and effectively acts to increase the yield strength. Therefore, by adding Al, the fatigue damage resistance can be greatly improved and the service life of the rail can be further extended. However, when the Al content exceeds 0.07 %, a large amount of oxides is produced in the steel, which ends up making the rail steel prone to fatigue damage. Therefore, in the case of adding Al, it is preferable to set the Al content to 0.07 % or less. The lower limit of the Al content is not particularly limited, yet from the viewpoint of improving the yield strength, it is preferable to set the Al content to 0.001 % or more.
[0030] B: 0.005 % or less
B precipitates as nitrides during and after rolling, and effectively acts to increase the yield strength by precipitation strengthening. Therefore, by adding B, the fatigue damage resistance can be greatly improved and the service life of the rail can be further extended. However, a B content beyond 0.005 % leads to an excessive increase in the yield strength, which ends up making the counterpart material, the wheel steel, prone to fatigue damage.
PO163542-PCT-ZZ (7/31)
-8Therefore, in the case of adding B, it is preferable to set the B content to 0.005 % or less. The lower limit of the B content is not particularly limited, yet from the viewpoint of improving the yield strength, it is preferable to set the B content to 0.0001 % or more.
[0031] Ti: 0.05 % or less
Ti forms precipitates as carbides, nitrides, and carbonitrides during and after rolling, and effectively acts to increase the yield strength by precipitation strengthening. Therefore, by adding Ti, the fatigue damage resistance can be greatly improved and the lift of the rail can be further extended. However, when the Ti content exceeds 0.05 %, coarse carbides, nitrides, or carbonitrides are formed, which ends up lowering the fatigue damage resistance of the rail. Therefore, in the case of adding Ti, it is preferable to set the Ti content to 0.05 % or less. The lower limit of the Ti content is not particularly limited, yet from the viewpoint of improving the yield strength, it is preferable to set the Ti content to 0.001 % or more.
[0032] [Chemical Composition of Wheel Steel]
C: 0.57 % or more and less than 0.85 %
C is an element that forms cementite in a pearlite structure and has the effect of securing yield strength and fatigue damage resistance. If the C content is less than 0.57 %, the yield strength decreases, making it difficult to obtain excellent fatigue damage resistance. On the other hand, if the C content is 0.85 % or more, pro-eutectoid cementite is formed at austenite grain boundaries at the time of transformation after hot rolling, and the fatigue damage resistance is remarkably deteriorated. Therefore, the C content is set to 0.57 % or more and less than 0.85 %.
[0033] Si: 0.10 % to 1.50 %
Si is an element that is added as a deoxidizer and as a pearlite-structure-strengthening element. To obtain the addition effect of Si, the Si content needs to be 0.10 % or more. On the other hand, a Si content beyond 1.50 % leads to an excessive increase in the yield strength, which ends up making the counterpart material, the rail steel, prone to fatigue damage. Therefore, the Si content is set in a range of 0.10 % to 1.50 %.
[0034] Mn: 0.40 % to 1.50 %
Mn is an element that contributes to achieving high yield strength of the wheel
PO163542-PCT-ZZ (8/31)
-9by decreasing the pearlite transformation temperature to refine the lamellar spacing. When the Mn content is less than 0.40 %, however, this effect cannot be obtained sufficiently. On the other hand, a Mn content beyond 1.50 % leads to an excessive increase in the yield strength, which ends up making the counterpart material, the rail steel, prone to fatigue damage. Therefore, the Mn content is set in a range of 0.40 % to 1.50 %.
[0035] Cr: 0.05 % to 1.50 %
Cr is an element that has the effect of increasing the pearlite equilibrium transformation temperature to refine the lamellar spacing and improving the yield strength by solid solution strengthening. When the Cr content is below 0.05 %, however, sufficient yield strength cannot be obtained. On the other hand, a Cr content beyond 1.50 % leads to an excessive increase in the yield strength, which ends up making the counterpart material, the rail steel, prone to fatigue damage. Therefore, the Cr content is set to 0.05 % to 1.50 %. [0036] The wheel steel in one embodiment of the present disclosure has a chemical composition containing the above components with the balance of Fe and inevitable impurities. Examples of the inevitable impurities include P and S, and up to 0.030 % of P and up to 0.030 % of S are allowable. On the other hand, a lower limit for the P content and the S content may be 0 % without limitation, yet it is more than 0 % in industrial terms. In addition, since excessively reducing the contents of P and S leads to an increase in the refining cost, the P content and the S content are preferably 0.0005 % or more. The chemical composition of the wheel steel of the present disclosure preferably consists of the above components and the balance of Fe and inevitable impurities, or alternatively, in addition to these, optional components as specified below. However, wheel steels containing other trace elements within a range not substantially affecting the action and effect of the present disclosure are also encompassed by the present disclosure. [0037] Optionally, the chemical composition of the wheel steel may further contain, by mass%, at least one selected from the group consisting of Cu: 1.0 % or less, Ni: 1.0 % or less, V: 0.30 % or less, Nb: 0.05 % or less, Mo: 0.5 % or less, W: 0.5 % or less, Al: 0.07 % or less, Ti: 0.05 % or less, and B: 0.005 % or less.
[0038] V: 0.30 % or less
PO163542-PCT-ZZ (9/31)
- ιόν is an element that has the effect of improving the yield strength by dispersing and precipitating in the matrix by forming carbides or nitrides. On the other hand, a V content beyond 0.30 % leads to an excessive increase in the yield strength, which ends up making the counterpart material, the rail steel, prone to fatigue damage. Also, since V is an expensive element, the cost of the wheel steel increases. Therefore, in the case of adding V, it is preferable to set the V content to 0.30 % or less. The lower limit of the V content is not particularly limited, yet from the viewpoint of improving the yield strength, it is preferable to set the V content to 0.001 % or more.
[0039] Cu: 1.0 % or less
Like Cr, Cu is an element having an effect of improving the yield strength by solid solution strengthening. However, when the Cu content exceeds 1.0 %, Cu cracking is liable to occur. Therefore, in the case of adding Cu, it is preferable to set the Cu content to 1.0 % or less. The lower limit of the Cu content is not particularly limited, yet from the viewpoint of improving the yield strength, it is preferable to set the Cu content to 0.001 % or more.
[0040] Ni: 1.0 % or less
Ni is an element that has an effect of improving the yield strength without deteriorating the ductility. In addition, in the case of adding Cu, it is preferable to add Ni because Cu cracking can be suppressed by the addition of Ni in combination with Cu. When the Ni content exceeds 1.0 %, however, the quench hardenability increases and martensite is formed, with the result that the fatigue damage resistance tends to decrease. Therefore, in the case of adding Ni, it is preferable to set the Ni content to 1.0 % or less. The lower limit of the Ni content is not particularly limited, yet from the viewpoint of improving the yield strength, it is preferable to set the Ni content to 0.001 % or more.
[0041] Nb: 0.05 % or less
Nb bonds to C or N in the steel to form precipitates as carbides, nitrides, or carbonitrides during and after rolling, and effectively acts to increase the yield strength. Therefore, by adding Nb, the fatigue damage resistance can be greatly improved and the service life of the wheel can be further extended. However, a Nb content beyond 0.05 % leads to an excessive increase in the yield strength, which ends up making the counterpart material, the rail steel,
PO163542-PCT-ZZ (10/31)
- 11 prone to fatigue damage. Therefore, in the case of adding Nb, it is preferable to set the Nb content to 0.05 % or less. The lower limit of the Nb content is not particularly limited, yet from the viewpoint of improving the yield strength, it is preferable to set the Nb content to 0.001 % or more.
[0042] Mo: 0.5 % or less
Mo is an element having an effect of improving the yield strength by solid solution strengthening. However, a Mo content beyond 0.5 % leads to an excessive increase in the yield strength, which ends up making the counterpart material, the rail steel, prone to fatigue damage. Therefore, in the case of adding Mo, it is preferable to set the Mo content to 0.5 % or less. The lower limit of the Mo content is not particularly limited, yet from the viewpoint of improving the yield strength, it is preferable to set the Mo content to 0.001 % or more.
[0043] W: 0.5 % or less
W is an element having an effect of improving the yield strength by solid solution strengthening. However, a W content beyond 0.5 % leads to an excessive increase in the yield strength, which ends up making the counterpart material, the rail steel, prone to fatigue damage. Therefore, in the case of adding W, it is preferable to set the W content to 0.5 % or less. The lower limit of the W content is not particularly limited, yet from the viewpoint of improving the yield strength, it is preferable to set the W content to 0.001 % or more.
[0044] Al: 0.07 % or less
Al bonds to N in the steel to form precipitates as nitrides during and after rolling, and effectively acts to increase the yield strength. Therefore, by adding Al, the fatigue damage resistance can be greatly improved and the service life of the wheel can be further extended. However, when the Al content exceeds 0.07 %, a large amount of oxides is produced in the steel, which ends up making the wheel steel prone to fatigue damage. Therefore, in the case of adding Al, it is preferable to set the Al content to 0.07 % or less. The lower limit of the Al content is not particularly limited, yet from the viewpoint of improving the yield strength, it is preferable to set the Al content to 0.001 % or more.
[0045] B: 0.005 % or less
PO163542-PCT-ZZ (11/31)
- 12B precipitates as nitrides during and after rolling, and effectively acts to increase the yield strength by precipitation strengthening. Therefore, by adding B, the fatigue damage resistance can be greatly improved and the service life of the wheel can be further extended. However, a B content beyond 0.005 % leads to an excessive increase in the yield strength, which ends up making the counterpart material, the rail steel, prone to fatigue damage. Therefore, in the case of adding B, it is preferable to set the B content to 0.005 % or less. The lower limit of the B content is not particularly limited, yet from the viewpoint of improving the yield strength, it is preferable to set the B content to 0.0001 % or more.
[0046] Ti: 0.05 % or less
Ti forms precipitates as carbides, nitrides, and carbonitrides during and after rolling, and effectively acts to increase the yield strength by precipitation strengthening. Therefore, by adding Ti, the fatigue damage resistance can be greatly improved and the service life of the wheel can be further extended. However, when the Ti content exceeds 0.05 %, coarse carbides, nitrides, or carbonitrides are formed, which ends up lowering the fatigue damage resistance of the wheel. Therefore, in the case of adding Ti, it is preferable to set the Ti content to 0.05 % or less. The lower limit of the Ti content is not particularly limited, yet from the viewpoint of improving the yield strength, it is preferable to set the Ti content to 0.001 % or more.
[0047] [Yield Strength Ratio YSr/YSw]
In the present disclosure, a rail steel and a wheel steel to be used as a rail and a wheel on an actual track, respectively, having the above-described chemical compositions are selected such that the rail comprises a head portion having a yield strength YSr, the wheel comprises a rim portion having a yield strength YSW, and a YSR/YSW ratio falls within a range of:
0.85 < YSr/YSw < 1.95 (1)·
In this case, the yield strength YSr of the rail is determined by collecting a tensile test specimen with a parallel portion of 0.25 inch or 0.5 inch as specified in ASTM A370 from a position as specified in AREMA Chapter 4, 2.1.3.4, and subjecting it to a tensile test. The yield strength YSw of the
PO163542-PCT-ZZ (12/31)
- 13 wheel is obtained by collecting a tensile test specimen similar to that obtained in the rail test from a position described in AAR Specification M-107/M-208, 3.1.1., and subjecting it to a tensile test.
[0048] The fatigue damage resistance of the rail steel and of the wheel steel depends on the yield strength of each. It is thus believed that the fatigue damage in the rail and the wheel can be suppressed by increasing the yield strength. However, if the ratio of the yield strength of the rail steel to the yield strength of the wheel steel is not in an appropriate range, the fatigue damage resistance is rather lowered due to the accumulation of fatigue layers. If the YSr/YSw ratio is below 0.85, the yield strength of the rail steel is too low, the yield strength of the wheel steel is too high, or both. If the yield strength of the rail steel is low, the fatigue damage resistance of the rail steel itself decreases, and the rail steel is consequently prone to fatigue damage. Also, if the yield strength of the wheel steel is high, fatigue layers accumulate in the rail steel as the counterpart material, which ends up causing fatigue damage to occur in the rail steel easily. If the YSR/YSW ratio is beyond 1.95, the yield strength of the wheel steel is too low, the yield strength of the rail steel is too high, or both. When the yield strength of the wheel steel is low, the fatigue damage resistance of the wheel steel itself decreases, and the wheel steel is consequently prone to fatigue damage. Also, if the yield strength of the rail steel is high, fatigue layers accumulate in the wheel steel as the counterpart material, which ends up causing fatigue damage to occur in the wheel steel easily. Therefore, the YSR/YSW ratio is set to 0.85 or more and 1.95 or less. The YSR/YSw ratio is preferably 0.86 or more. The YSR/YSW ratio is preferably 1.90 or less.
[0049] [Yield Strength YSR at Head Portion of Rail]
Since the fatigue damage resistance of the rail itself can be further enhanced by increasing the yield strength YSR at the head portion of the rail, YSR is set to 830 MPa or more. Although no upper limit is placed on YSR, excessively increasing YSR makes it difficult to satisfy the condition of formula (1). Thus, a preferred upper limit is 1200 MPa.
[0050] When a rail is produced by hot rolling a steel raw material into a rail shape and cooling it, the yield strength YSR at the head portion of the rail can be adjusted by controlling the heating temperature before hot rolling and the
PO163542-PCT-ZZ (13/31)
- 14cooling rate in cooling after hot rolling. In other words, since the yield strength YSr becomes higher as the heating temperature becomes higher and the cooling rate after hot rolling becomes higher, the heating temperature and the cooling rate may be adjusted for the targeted YSR.
[0051] [Yield Strength YSw at Rim Portion of Wheel]
By increasing the yield strength YSw at the rim portion of the wheel, the fatigue damage resistance of the wheel itself can be enhanced. Therefore, the YSw is set to 580 MPa or more. Although no upper limit is placed on YSw, excessively increasing YSw makes it difficult to satisfy the condition of formula (1). Thus, a preferred upper limit is 1000 MPa.
[0052] When a wheel is formed by hot working such as hot rolling and hot forging, the yield strength YSw at the rim portion of the wheel can be adjusted by controlling the heating temperature before hot working and the cooling rate in cooling after hot working. In other words, since the yield strength YSw becomes higher as the heating temperature becomes higher and the cooling rate after hot rolling becomes higher, the heating temperature and the cooling rate may be adjusted for the targeted YSW· [0053] [Steel Microstructure of Rail Steel and Wheel Steel]
In the rail steel, the steel microstructure of the head portion of the rail is preferably a pearlite structure. This is because the pearlite structure has better fatigue damage resistance than the tempered martensite structure and the bainite structure.
[0054] Also, in the wheel steel, the steel microstructure of the rim portion of the wheel is preferably a pearlite structure. This is because a pearlite structure has excellent fatigue damage resistance as compared with the tempered martensite structure and the bainite structure as described above. [0055] In order to make the steel microstructure of the head portion of the rail steel into a pearlite structure, the steel raw material is heated to 1000 °C to 1300 °C and then hot rolled. Then, air cooling is performed to 400 °C at a cooling rate of 0.5 °C/s to 3 °C/s.
[0056] Further, in order to make the steel microstructure of the rim portion of the wheel steel into a pearlite structure, the steel material is heated to 900 °C to 1100 °C and then hot forged. Then, air cooling is performed to 400 °C at a cooling rate of 0.5 °C/s to 3 °C/s.
PO163542-PCT-ZZ (14/31)
- 15 EXAMPLES [0057] We evaluated the effect of the yield strength ratio YSR/YSW on the occurrence of fatigue damage. Evaluation of fatigue damage is desirably carried out by using rails and wheels on an actual track, yet this process requires an extremely long test time. Therefore, in the examples below, the occurrence of fatigue damage was evaluated using test specimens fabricated from a rail steel and a wheel steel, respectively, and carrying out tests simulating a set of actual contact conditions between the rail and the wheel using a two-cylinder testing machine. At that time, the rail steel specimen and the wheel steel specimen were produced under a set of conditions simulating the head portion of the rail and the rim portion of the wheel, respectively. The specific production conditions and test methods are as follows.
[0058] (Example 1)
In this case, 100 kg of steels having the chemical compositions in Table 1 were each subjected to vacuum melting and hot rolled to a thickness of 80 mm. Each rolled material thus obtained was cut to a length of 150 mm, heated to 1000 °C to 1300 °C, and hot rolled to a final sheet thickness of 12 mm. Then, air cooling was performed to 400 °C at a cooling rate of 0.5 °C/s to 3 °C/s, and then allowed to cool to obtain a rail steel. At this time, the yield strength of the finally obtained rail steel was controlled by adjusting the heating temperature and the cooling rate before the hot rolling.
[0059] Similarly, 100 kg of steels having the chemical compositions in Table 2 were each subjected to vacuum melting and hot rolled to a thickness of 80 mm. Each rolled material thus obtained was cut to a length of 150 mm, heated to 900 °C to 1100 °C, and hot rolled to a final sheet thickness of 12 mm. Then, air cooling was performed to 400 °C at a cooling rate of 0.5 °C/s to 3 °C/s, and then allowed to cool. At this time, the yield strength of the finally obtained wheel steel was controlled by adjusting the heating temperature and the cooling rate before the hot rolling.
[0060] · Yield strength
The yield strength of each rail steel and wheel steel thus obtained was evaluated by a tensile test in accordance with ASTM A370. From each rail
PO163542-PCT-ZZ (15/31)
- 16steel and wheel steel, a tensile test specimen having a parallel portion diameter of 0.25 inch (6.35 mm) as prescribed in ASTM A370 was collected and subjected to a tensile test at a tensile rate of 1 mm/min, where a 0.2 % proof stress was determined from the stress-strain curve and used as the yield strength. The measured values are presented in Table 2.
[0061] • Steel microstructure
After polishing the surface of each obtained rail steel and wheel steel to a mirror surface, it was etched with nital, and microstructure observation was carried out at xlOO magnification.
[0062] · Fatigue damage
Test specimens with a diameter of 30 mm were prepared from each obtained rail steel and wheel steel with a contact surface being a curved surface having a radius of curvature of 15 mm. Then, in each combination of a rail steel and a wheel steel listed in Table 3, the occurrence of fatigue damage was evaluated using a two-cylinder testing machine. Tests were conducted at a contact pressure of 2.2 GPa and a slip rate of -20 % under oil lubrication condition, and the number of revolutions at the time when peeling (fatigue damage) occurred was counted as presented in Table 3. The number of revolutions can be regarded as an index of fatigue damage life of the rail and the wheel. Since it takes a long time to continue the test until peeling occurs, in this example, in the case where the rail steel was peeled off at less than 1,728,000 revolutions and where the wheel steel was peeled off at less than 2,160,000 revolutions, it was judged that satisfactory fatigue damage resistance could not be obtained with that rail steel and wheel steel combination, and the test was interrupted. In this case, for members that did not peel off, the number of revolutions in Table 2 is set to On the other hand, the fatigue damage resistance was determined to be good when the number of revolutions was 1,728,000 or more for rail steels and 2,160,000 or more for wheel steels, as indicated by no peeling in Table 3.
[0063] It can be seen from the results in Table 3 that, the fatigue damage in a rail and a wheel can be effectively suppressed by selecting a rail steel and a wheel steel such that their chemical compositions and yield strength ratio YSr/YSw satisfy the conditions disclosed herein. On the other hand, it will be appreciated that in those combinations not satisfying the conditions of the
PO163542-PCT-ZZ (16/31)
- 17present disclosure, peeling occurs in a short time and fatigue damage tends to occur easily.
[0064]
Table 1
Steel No. | Chemical composition of rail steel (mass%)* | Remarks | |||||
C | Si | Mn | P | s | Cr | ||
Rl-1 | 0.82 | 1.50 | 0.49 | 0.014 | 0.007 | 0.26 | Conforming Steel |
Rl-2 | 0.83 | 0.25 | 0.85 | 0.005 | 0.007 | 0.61 | Conforming Steel |
Rl-3 | 0.70 | 0.41 | 0.40 | 0.003 | 0.006 | 1.50 | Conforming Steel |
Rl-4 | 0.83 | 0.87 | 0.47 | 0.003 | 0.006 | 1.46 | Conforming Steel |
Rl-5 | 0.84 | 0.88 | 0.46 | 0.016 | 0.005 | 0.79 | Conforming Steel |
Rl-6 | 0.83 | 0.87 | 0.47 | 0.003 | 0.006 | 1.46 | Conforming Steel |
Rl-7 | 0.79 | 0.98 | 0.71 | 0.005 | 0.007 | 0.27 | Conforming Steel |
Rl-8 | 0.81 | 0.69 | 0.56 | 0.015 | 0.007 | 0.79 | Conforming Steel |
Rl-9 | 0.77 | 0.52 | 0.78 | 0.012 | 0.007 | 0.75 | Conforming Steel |
Rl-10 | 0.81 | 0.71 | 0.40 | 0.004 | 0.004 | 0.93 | Conforming Steel |
Rl-11 | 0.71 | 1.16 | 1.34 | 0.016 | 0.004 | 0.88 | Conforming Steel |
Rl-12 | 0.84 | 1.06 | 0.83 | 0.019 | 0.006 | 0.05 | Conforming Steel |
Rl-13 | 0.84 | 0.48 | 0.71 | 0.016 | 0.004 | 0.32 | Conforming Steel |
Rl-14 | 0.68 | 0.25 | 0.81 | 0.015 | 0.006 | 0.05 | Comparative Steel |
Rl-15 | 0.86 | 0.88 | 0.81 | 0.015 | 0.007 | 1.39 | Comparative Steel |
Rl-16 | 0.72 | 0.05 | 0.81 | 0.015 | 0.005 | 0.21 | Comparative Steel |
Rl-17 | 0.82 | 1.52 | 0.82 | 0.014 | 0.005 | 0.99 | Comparative Steel |
Rl-18 | 0.72 | 0.25 | 0.35 | 0.015 | 0.005 | 0.18 | Comparative Steel |
Rl-19 | 0.84 | 0.29 | 1.52 | 0.011 | 0.005 | 0.99 | Comparative Steel |
Rl-20 | 0.81 | 0.63 | 0.81 | 0.006 | 0.003 | 0,01 | Comparative Steel |
Rl-21 | 0.85 | 0.59 | 0.81 | 0.007 | 0.003 | 1.52 | Comparative Steel |
Rl-22 | 0.70 | 0.55 | 1.50 | 0.010 | 0.005 | 0.27 | Conforming Steel |
Rl-23 | 0.84 | 0.11 | 0.74 | 0.005 | 0.007 | 0.90 | Conforming Steel |
Rl-24 | 0.83 | 0.31 | 0.81 | 0.005 | 0.007 | 0.33 | Conforming Steel |
Rl-25 | 0.84 | 0.96 | 0.95 | 0.005 | 0.007 | 0.96 | Conforming Steel |
* The balance consists of Fe and inevitable impurities.
PO163542-PCT-ZZ (17/31)
- 18[0065]
Table 2
Steel No. | Chemical composition of wheel steel (mass%)* | Remarks | |||||
C | Si | Mn | P | s | Cr | ||
Wl-1 | 0.84 | 1.01 | 1.15 | 0.012 | 0.002 | 0.09 | Conforming Steel |
Wl-2 | 0.65 | 0.29 | 1.50 | 0.015 | 0.008 | 0.20 | Conforming Steel |
Wl-3 | 0.81 | 0.75 | 0.70 | 0.019 | 0.004 | 0.34 | Conforming Steel |
Wl-4 | 0.84 | 1.50 | 0.40 | 0.007 | 0.010 | 0.33 | Conforming Steel |
Wl-5 | 0.78 | 0.25 | 0.80 | 0.012 | 0.005 | 1.50 | Conforming Steel |
Wl-6 | 0.74 | 0.27 | 0.70 | 0.019 | 0.007 | 0.22 | Conforming Steel |
Wl-7 | 0.85 | 1.00 | 0.85 | 0.008 | 0.009 | 0.39 | Conforming Steel |
Wl-8 | 0.78 | 0.10 | 0.71 | 0.005 | 0.003 | 0.24 | Conforming Steel |
Wl-9 | 0.79 | 0.26 | 0.71 | 0.015 | 0.009 | 0.22 | Conforming Steel |
Wl-10 | 0.69 | 0.33 | 0.81 | 0.019 | 0.003 | 0.22 | Conforming Steel |
Wl-11 | 0.84 | 0.28 | 0.65 | 0.003 | 0.001 | 0.05 | Conforming Steel |
Wl-12 | 0.80 | 0.22 | 0.74 | 0.015 | 0.007 | 0.20 | Conforming Steel |
Wl-13 | 0.76 | 0.21 | 0.70 | 0.004 | 0.009 | 0.21 | Conforming Steel |
Wl-14 | 0.56 | 0.69 | 0.81 | 0.011 | 0.005 | 0.31 | Comparative Steel |
Wl-15 | 0.86 | 0.39 | 0.91 | 0.015 | 0.006 | 0.77 | Comparative Steel |
Wl-16 | 0.72 | 0.05 | 0.81 | 0.015 | 0.005 | 0.19 | Comparative Steel |
Wl-17 | 0.82 | 1.52 | 0.82 | 0.014 | 0.005 | 0.99 | Comparative Steel |
Wl-18 | 0.72 | 0.25 | 0.35 | 0.015 | 0.005 | 0.18 | Comparative Steel |
Wl-19 | 0.84 | 0.29 | 1.52 | 0.011 | 0.005 | 0.99 | Comparative Steel |
Wl-20 | 0.74 | 0.21 | 0.77 | 0.006 | 0.003 | 0.01 | Comparative Steel |
Wl-21 | 0.85 | 0.59 | 0.81 | 0.007 | 0.003 | 1.52 | Comparative Steel |
Wl-22 | 0.75 | 0.15 | 0.75 | 0.004 | 0.005 | 0.19 | Conforming Steel |
Wl-23 | 0.68 | 0.23 | 0.71 | 0.014 | 0.003 | 0.24 | Conforming Steel |
Wl-24 | 0.79 | 0.95 | 0.95 | 0.014 | 0.003 | 0.74 | Conforming Steel |
Wl-25 | 0.69 | 0.31 | 0.69 | 0.013 | 0.007 | 0.34 | Conforming Steel |
* The balance consists of Fe and inevitable impurities.
PO163542-PCT-ZZ (18/31) [0066]
Table 3
Remarks | Example | Example | Example | Example | Example | Example | Example | Example | Example | Example | Example | Example | Example | Comparative Example | Comparative Example | Comparative Example | Comparative Example | Comparative Example | |
Number of revolutions when peeling occurred | Wheel | no peeling | no peeling | no peeling | no peeling | no peeling | no peeling | no peeling | no peeling | no peeling | no peeling | no peeling | no peeling | no peeling | 472500 | 481500 | |||
Rail | no peeling | no peeling | no peeling | no peeling | no peeling | no peeling | no peeling | no peeling | no peeling | no peeling | no peeling | no peeling | no peeling | 1080000 | 1231200 | 1299600 | |||
Yield strength ratio YSr/YSw | 1.23 | 1.38 | oo | 1.95 | 1.40 | 09'1 | 0.85 | 0.94 | hy | 60Ί | 1.02 | 0.95 | CH | 0.74 | 2.02 | 18Ό | 2.04 | 0.82 | |
Wheel | Yield strength YSW (MPa) | 709 | 646 | 727 | 582 | 678 | Γ— | cy oo Os | 953 | 661 | 832 | 983 | 922 | 709 | 1055 | CH m KY | m KT Os | 532 | 953 |
Steel microstructure* | CL | CL | CL | CL | CL | Cl | CL | CL | CL | CL | CL | CL | CL | CL | CL | CL | CL | CL | |
Steel No. | Wl-12 | Wl-13 | Wl-ll | Wl-10 | Wl-8 | Wl-9 | Wl-7 | Wl-l | Wl-2 | Wl-3 | Wl-7 | Wl-4 | Wl-12 | Wl-5 | Wl-23 | Wl-l | Wl-23 | Wl-l | |
Rail | Yield strength YSR(MPa) | vy Γ- ΟΟ | 068 | 098 | 1135 | 948 | 1135 | KT m oo | 896 | 865 | 907 | 1006 | 877 | 857 | 780 | 1074 | 770 | 1083 | 781 |
Steel microstructure* | CL | CL | CL | CL | CL | CL | CL | CL | CL | CL | CL | CL | CL | CL | CL | CL | CL | CL | |
Steel No. | Rl-1 | Rl-2 | Rl-3 | Rl-4 | Rl-5 | Rl-6 | Rl-7 | Rl-8 | Rl-9 | Rl-10 | Rl-ll | Rl-12 | Rl-13 | Rl-14 | Rl-15 | Rl-16 | Rl-17 | Rl-18 | |
No. | - | CH | C-Y | 'T | VY | SO | Γ- | OO | Os | o | CH | CC | Tt | KY | SO | Γ- | OO |
P: peariite, M: martensite.
PO163542-PCT-ZZ (19/31)
Table 3 (cont'd)
Remarks | Comparative Example | Comparative Example | Comparative Example | Example | Example | Example | Comparative Example | Comparative Example | Comparative Example | Comparative Example | Comparative Example | Comparative Example | Comparative Example | Comparative Example | g- s | Example | Comparative Example | Comparative Example | |
Number of revolutions when peeling occurred | Wheel | 472500 | 481500 | no peeling | no peeling | no peeling | 733500 | 688500 | 666000 | 697500 | I3 <u <u CU g | no peeling | 742500 | ||||||
Rail | 1436400 | no peeling | no peeling | no peeling | 1522800 | 1458000 | 1666800 | 1342800 | <D <U CU s | no peeling | 1386000 | ||||||||
Yield strength ratio YSR/YSW | 1.96 | 0,84 | 2,01 | Tt- | 880 | 1.83 | OOI OS | 0.83 | 96'1 | 0.70 | 2.00 | 0.79 | r-~-| OS | 0.70 | o s© | 1.48 | 0,84 | 96Ί | |
Wheel | Yield strength YSW (MPa) | 532 | 953 | 532 | 727 | 1055 | 621 | 452 | 1028 | 579 | 1166 | 502 | 1179 | 576 | 1221 | r- CM SO | 580 | 666 | 583 |
Steel microstructure* | CU | CU | CU | CU | CU | CU | CU | CU | CU | CU | CU | CU | CU | CU | CU | CU | CU | CU | |
Steel No. | Wl-23 | Wl-1 | Wl-23 | Wl-12 | Wl-5 | Wl-6 | Wl-14 | Wl-15 | Wl-16 | Wl-17 | Wl-18 | Wl-19 | Wl-20 | Wl-21 | CM CM ίϊ | Wl-23 | Wl-23 | Wl-23 | |
Rail | Yield strength YSR(MPa) | 1043 | 802 | 1068 | 830 | 931 | 1135 | 896 | 857 | 1135 | 822 | 1006 | 931 | 1135 | 857 | so o o | 857 | 838 | 1144 |
Steel microstructure* | CU | CU | CU | CU | CU | CU | CU | CU | CU | CU | CU | CU | CU | CU | CU | CU | CU | CU | |
Steel No. | Rl-19 | Rl-20 | Rl-21 | Rl-22 | Rl-23 | Rl-4 | Rl-8 | Rl-13 | Rl-6 | Rl-22 | Rl-11 | Rl-23 | Rl-4 | Rl-13 | s | Rl-13 | Rl-24 | Rl-25 | |
No. | Os | o CM | CM | CM CM | CO CM | CM | CM | Ο CM | Γ— CM | CO CM | Os CM | o co | CO | CM CO | co co | co | UO CO | SO co |
P: pearlite, M: martensite.
PO163542-PCT-ZZ (20/31)
-21 [0067] (Example 2)
Tests were conducted under the same conditions as in Example 1 except that rail steels having the compositions listed in Table 4 and wheel steels having the compositions in Table 5 were used. Table 6 lists the rail steel and wheel steel combinations used and the evaluation results. It can be seen from these results that the fatigue damage in a rail and a wheel can be effectively suppressed by selecting a rail steel and a wheel steel such that their chemical compositions and yield strength ratio YSr/YSw satisfy the conditions disclosed herein.
PO163542-PCT-ZZ (21/31) [0068]
Table 4
Remarks | Conforming Steel | Conforming Steel | Conforming Steel | Conforming Steel | Conforming Steel | Conforming Steel | Conforming Steel | Conforming Steel | |
Chemical composition of rail steel (mass%)* | H | 1 | 1 | 1 | 1 | 1 | 0.05 | ||
m | 1 | 1 | 1 | 1 | 1 | 1 | 0.003 | 1 | |
£ | 1 | 1 | 1 | 1 | 1 | 0.20 | 1 | 1 | |
< | 1 | 1 | 1 | 1 | 1 | 0.07 | |||
Nb | 1 | 1 | 0.04 | 1 | 1 | 1 | 1 | 1 | |
> | 0.05 | 0.30 | 1 | 1 | 1 | 1 | 1 | 0.05 | |
Mo | 1 | 1 | m o | 1 | |||||
Z | 1 | 1 | 1 | 1 | o | 1 | 1 | 1 | |
Cu | 1 | 1 | 1 | 1 | •ZT O | 1 | 1 | 1 | |
Cr | 0.79 | 0.74 | 0.25 | 0.29 | 0.62 | 0.29 | 0.45 | 0.79 | |
CZ) | 0.005 | 0.004 | 0.005 | 0.004 | 0.005 | 0.005 | 0.005 | 0.005 | |
Ct-I | 0.014 | 800Ό | 900Ό | 0.003 | 110Ό | 0.004 | 0.005 | 110Ό | |
Mn | 0.55 | 0.61 | o | 1.05 | 0.55 | 1.20 | 0.55 | 0.56 | |
Z | 0.55 | 0.51 | 0.25 | 0.35 | 0.55 | 0.25 | 88Ό | 0.95 | |
o | 0.84 | 0.84 | 0.84 | 0.84 | 0.84 | 0.84 | 0.84 | 0.84 | |
Steel No. | R2-1 | R2-2 | R2-3 | R2-4 | R2-5 | R2-6 | R2-7 | R2-8 |
<L>
.s c
.23
C/5
PO163542-PCT-ZZ (22/31) [0069]
Table 5
Remarks | Conforming Steel | | Conforming Steel | Conforming Steel | | Conforming Steel | | Conforming Steel | Conforming Steel | | Conforming Steel | | Conforming Steel | |
Chemical composition of wheel steel (mass%)* | P | 1 | 1 | 1 | 1 | 1 | 0.05 | 1 | 1 |
m | 1 | 0.003 | 1 | ||||||
£ | 1 | 1 | 1 | 1 | 0.20 | 1 | 1 | 1 | |
IV | 0.05 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | |
Nb | 1 | 0.05 | 0.05 | ||||||
> | 0.10 | 1 | 1 | 0.20 | 1 | 1 | 1 | 0.05 | |
Mo | 1 | 1 | 0.2 | 1 | 1 | 1 | 1 | 1 | |
Ni | 1 | O | 1 | 1 | 01Ό | ||||
Cu | 1 | 0.5 | 1 | 1 | 1 | 1 | 1 | ||
Cr | 0.25 | 0.20 | 0.28 | 0.25 | 0.74 | 0.22 | 0.35 | 0.29 | |
CZ5 | 0.005 | 800Ό | o o o | 600Ό | 0.005 | 0.007 | 0.007 | 0.003 | |
0.012 | 0.015 | 05 o o | 0.007 | 0.012 | 610Ό | 800Ό | 0.005 | ||
Mn | o 00 © | 0.75 | 0.78 | o 00 o | 08'0 | 0.70 | 0.84 | 0.82 | |
0.25 | 0.21 | 0.35 | 0.33 | 0.25 | 0.27 | 66Ό | © | ||
υ | 0.78 | 0.79 | 18Ό | -0 00 o | 0.78 | 00 o | 0.84 | 0.79 | |
Steel No. | W2-1 | CM 1 rq | 1 ΓΊ | I W2-4 | W2-5 | W2-6 | r- 1 Γ1 | W2-8 |
σ3 .s g
C ¢3 <L>
H
PO163542-PCT-ZZ (23/31)
-24[0070]
Table 6
ΖΛ | Example | Example | Example | Example | Example | Example | Example | Example | |
¢4 | |||||||||
On | 0β | on | on | on | on | on | on | ||
co Ό fi <D | o | lin | lin | lin | lin | lin | lin | lin | lin |
Q bj | <1> | <υ | <1> | <1> | <υ | o | <L> | ||
-fi | <υ | <υ | <υ | <υ | <υ | <υ | <D | ||
-3 o | CL | CL | CL | CL | CL | CL | CL | CL | |
O Q | o | o | o | o | O | o | O | o | |
r of rev eeling o | fi | fi | fi | fi | fi | fi | fi | fi | |
on | on | on | on | op | on | on | on | ||
£ a. | r= zS | ||||||||
fi fi | <υ | <υ | 0) | <υ | <υ | <υ | <υ | <υ | |
S Q | <υ | <υ | <υ | <υ | <υ | <υ | |||
fin | CL | CL | CL | CL | CL | CL | CL | CL | |
£ ? | o | o | o | o | o | o | o | o | |
fi | fi | fi | fi | fi | fi | fi | fi | ||
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PO163542-PCT-ZZ (24/31)
-25 [0071] (Example 3)
Tests were conducted under the same conditions as in Example 1 except that rail steels having the chemical compositions listed in Table 7 and wheel steels having the compositions in Table 8 were used. In addition, the Vickers hardness HR of the finally obtained rail steel and the Vickers hardness Hw of the finally obtained wheel steel were measured using a Vickers hardness testing machine with a load of 98 N, and the ratio HR/HW of the hardness HR of the rail steel to the hardness Hw of the wheel steel was determined. Table 9 lists the rail steel and wheel steel combinations used and the evaluation results.
[0072] Again, it can be seen from these results that the fatigue damage in a rail and a wheel can be effectively suppressed by selecting a rail steel and a wheel steel such that their chemical compositions and yield strength ratio YSR/YSw satisfy the conditions disclosed herein. In addition, as described in PTL 2, it is found that even with the use of a combination of a rail steel and a wheel steel in which the ratio HR/HW of the hardness HR of the rail steel to the hardness Hw of the wheel steel is 1.00 or more and 1.30 or less is used, the fatigue damage resistance of the rail and the wheel is inferior if the yield strength of the rail steel is less than 830 MPa, the yield strength of the wheel steel is less than 580 MPa, and the yield strength ratio YSR/YSw is out of the range of 0.85 to 1.95 disclosed herein. It is also understood that the fatigue damage resistance of the wheel is inferior when the wheel steel has a steel microstructure other than pearlite.
PO163542-PCT-ZZ (25/31)
-26[0073]
Table 7
Steel No. | Chemical composition of rail steel (mass%)* | Remarks | ||||||
C | Si | Mn | P | s | Cr | Others | ||
R3-1 | 0.84 | 0.55 | 0.55 | 0.014 | 0.005 | 0.79 | - | Conforming Steel |
R3-2 | 0.84 | 0.95 | 0.61 | 0.008 | 0.004 | 0.74 | - | Conforming Steel |
R3-3 | 0.80 | 0.15 | 1.10 | 0.006 | 0.005 | 0.25 | - | Conforming Steel |
R3-4 | 0.70 | 0.15 | 1.05 | 0.003 | 0.004 | 0.29 | - | Conforming Steel |
R3-5 | 0.80 | 0.55 | 0.55 | 0.011 | 0.005 | 0.55 | - | Conforming Steel |
R3-6 | 0.84 | 0.25 | 1.20 | 0.004 | 0.005 | 0.29 | - | Conforming Steel |
R3-7 | 0.84 | 0.88 | 0.55 | 0.005 | 0.005 | 0.51 | - | Conforming Steel |
R3-8 | 0.85 | 0.90 | 0.61 | 0.011 | 0.004 | 0.81 | - | Conforming Steel |
R3-9 | 0.85 | 1.50 | 0.22 | 0.015 | 0.006 | 1.22 | - | Conforming Steel |
R3-10 | 0.85 | 0.25 | 0.81 | 0.015 | 0.006 | 0.25 | - | Conforming Steel |
R3-11 | 0.73 | 0.50 | 0.65 | 0.015 | 0.012 | 0.45 | - | Conforming Steel |
* The balance consists of Fe and inevitable impurities.
[0074]
Table 8
Steel No. | Chemical composition of wheel steel (mass%)* | Remarks | ||||||
C | Si | Mn | P | S | Cr | Others | ||
W3-1 | 0.78 | 0.25 | 0.80 | 0.012 | 0.005 | 0.25 | - | Conforming Steel |
W3-2 | 0.79 | 0.21 | 0.75 | 0.015 | 0.008 | 0.20 | - | Conforming Steel |
W3-3 | 0.81 | 0.35 | 0.78 | 0.019 | 0.004 | 0.28 | - | Conforming Steel |
W3-4 | 0.79 | 0.99 | 0.84 | 0.008 | 0.007 | 0.35 | - | Conforming Steel |
W3-5 | 0.69 | 0.25 | 0.75 | 0.012 | 0.005 | 0.27 | - | Conforming Steel |
W3-6 | 0.68 | 0.27 | 0.70 | 0.019 | 0.007 | 0.22 | - | Conforming Steel |
W3-7 | 0.84 | 0.33 | 0.80 | 0.007 | 0.009 | 0.25 | - | Conforming Steel |
W3-8 | 0.79 | 0.11 | 0.82 | 0.005 | 0.003 | 0.29 | - | Conforming Steel |
W3-9 | 0.63 | 0.69 | 0.81 | 0.011 | 0.005 | 0.39 | - | Conforming Steel |
W3-10 | 0.85 | 0.39 | 0.91 | 0.015 | 0.006 | 0.72 | - | Conforming Steel |
W3-11 | 0.75 | 0.40 | 0.20 | 0.021 | 0.002 | 0.85 | NkO.10 | Conforming Steel |
* The balance consists of Fe and inevitable impurities.
PO163542-PCT-ZZ (26/31) [0075]
Table 9
Remarks | Example | | Example | | Comparative Example | | Comparative Example | | Example | | Comparative Example | | Comparative Example | | Example | | Comparative Example | | Comparative Example | | Comparative Example | | |
Number of revolutions when peeling occurred | Wheel | no peeling | | no peeling | | no peeling | | 481500 | 472500 | no peeling | | 481500 | 1440000 | |||
Rail | no peeling | no peeling | 1436400 | 1080000 | no peeling | no peeling | 1436400 | |||||
Hardness ratio HR/HW | MD | 1.20 | 80Ί | © | 00Ί | 1.22 | 1.29 | 60Ί | 1.29 | 00Ί | (-- | |
Yield strength ratio YSR/YSW | 1.35 | MD | © | © | 1.57 | 69T | MD | 1.96 | 0.84 | 1.03 | ||
Wheel | Hardness Hw HV | 359 | 357 | 343 | 342 | MD OO cd | 330 | 314 | 400 | CD MD CD | 400 | 360 |
Steel microstructure* | a. | a. | a. | a. | a. | a. | a. | a- | a. | a- | Tempering M | |
Yield strength YSW (MPa) | 776 | 727 | 716 | 701 | 823 | 569 | CDI CD MD | s oo | Tfr OC MD | 998 | © 00 oo | |
Steel No. | W3-3 | W3-8 | W3-1 | W3-2 | W3-7 | W3-5 | W3-6 | W3-4 | W3-9 | W3-10 | W3-11 | |
Rail | Hardness HR HV | 412 | 429 | 371 | 346 | 386 | 403 | 406 | 435 | MD MD Tj- | 400 | 420 |
Steel microstructure* | a. | a. | a. | a. | a. | a. | a. | a. | a. | a. | a. | |
Yield strength YSR (MPa) | 924 | 978 | 823 | 773 | cd oo | 896 | 899 | 1008 | 1143 | 00 CD CO | 016 | |
Steel No. | R3-1 | R3-2 | R3-3 | 2 | R3-5 | R3-6 | R3-7 | 00 2 | R3-9 | R3-10 | R3-11 | |
No. | - | CM | CD | MD | SO | r-~ | 00 | Os | © |
PO163542-PCT-ZZ (27/31)
-282016374421 11 Jul 2019
REFERENCE SIGNS LIST [0076] wheel material
2 rail material [0077]
The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.
[0078]
Throughout this specification and the claims which follow, unless the context requires otherwise, the word comprise, and variations such as comprises and comprising, will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.
Claims (3)
- THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:1. A method for selecting a rail steel and a wheel steel comprising:selecting a rail steel and a wheel steel to be used as a rail and a wheel on an actual track, respectively, the rail steel having a chemical composition containing, by mass%,C: 0.70 % or more and less than 0.85 %,Si: 0.10 % to 1.50 %,Mn: 0.40 % to 1.50 %, andCr: 0.05 % to 1.50 %, with the balance of Fe and inevitable impurities, the wheel steel having a chemical composition containing, by mass%,C: 0.57 % or more and less than 0.85 %,Si: 0.10 % to 1.50 %,Mn: 0.40 % to 1.50 %, andCr: 0.05 % to 1.50 %, with the balance of Fe and inevitable impurities, such that the rail comprises a head portion having a yield strength YSr of 830 MPa or more, the wheel comprises a rim portion having a yield strength YSw of 580 MPa or more, and a ratio YSr/YSw of the yield strength YSr at the head portion of the rail to the yield strength YSw at the rim portion of the wheel falls within a range of:0.85 < YSr/YSw < 1.95 (1)
- 2. The method for selecting a rail steel and a wheel steel according to claim 1, wherein the chemical composition of the rail steel further contains, by mass%, at least one selected fromCu: 1.0 % or less,Ni: 1.0 % or less,PO163542-PCT-ZZ (29/5)-302016374421 11 Jul 2019V: 0.30 % or less,Nb: 0.05 % or less,Mo: 0.5 % or less,W: 0.5 % or less,5 Al: 0.07 % or less,Ti: 0.05 % or less, and B: 0.005 % or less.
- 3. The method for selecting a rail steel and a wheel steel 10 according to claim 1 or 2, wherein the chemical composition of the wheel steel further contains, by mass%, at least one selected from Cu: 1.0 % or less,Ni: 1.0 % or less,V: 0.30 % or less,15 Nb: 0.05 % or less,Mo: 0.5 % or less,W: 0.5 % or less,Al: 0.07 % or less,Ti: 0.05 % or less, and20 B: 0.005 % or less.PO163542-PCT-ZZ (30/5)
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JP6822575B2 (en) * | 2018-03-30 | 2021-01-27 | Jfeスチール株式会社 | Rails and their manufacturing methods |
AU2019347433B2 (en) * | 2018-09-28 | 2022-01-06 | Nippon Steel Corporation | Railway wheel |
CN111254248B (en) * | 2020-01-21 | 2021-12-24 | 鞍钢股份有限公司 | Method for controlling total aluminum of heavy rail steel U75V |
AU2021243639B2 (en) * | 2020-03-26 | 2023-11-02 | Nippon Steel Corporation | Railway wheel |
CN112063929B (en) * | 2020-09-21 | 2021-06-22 | 江阴方圆环锻法兰有限公司 | Novel bearing forging for shield tunneling machine and forging method thereof |
WO2022106864A1 (en) * | 2020-11-17 | 2022-05-27 | Arcelormittal | Steel for rails and a method of manufacturing of a rail thereof |
CN113667901A (en) * | 2021-08-23 | 2021-11-19 | 智奇铁路设备有限公司 | Material for locomotive wheels |
JPWO2023062886A1 (en) * | 2021-10-14 | 2023-04-20 | ||
CN114107823A (en) * | 2021-11-30 | 2022-03-01 | 宝武集团马钢轨交材料科技有限公司 | Steel for high-speed wheel, heat treatment method of steel and method for preparing high-speed wheel by using steel |
CN114645115B (en) * | 2022-04-25 | 2023-06-27 | 马鞍山钢铁股份有限公司 | Wheel with hardness grade of more than 360HB for heavy-duty truck, heat treatment method and production method thereof |
CN115679217B (en) * | 2022-11-11 | 2024-02-13 | 山东钢铁股份有限公司 | High-carbon steel for crane wheel body and preparation method thereof |
CN115896632B (en) * | 2022-12-09 | 2024-01-30 | 宝武集团马钢轨交材料科技有限公司 | Corrosion-resistant and wear-resistant wheel and production method thereof |
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